From: khsieh@codeaurora.org
To: Stephen Boyd <swboyd@chromium.org>
Cc: agross@kernel.org, bjorn.andersson@linaro.org,
robdclark@gmail.com, sean@poorly.run, vkoul@kernel.org,
abhinavk@codeaurora.org, aravindh@codeaurora.org,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/2] drm/msm/dp: handle irq_hpd with sink_count = 0 correctly
Date: Thu, 20 May 2021 15:39:09 -0700 [thread overview]
Message-ID: <5d341df202facb3240a72cfb35e18167@codeaurora.org> (raw)
In-Reply-To: <CAE-0n51+mbCAqWWTOMDA4Rx_=96V4tK8g+UWVZ-nnp50dFzRPA@mail.gmail.com>
On 2021-05-20 14:28, Stephen Boyd wrote:
> Quoting khsieh@codeaurora.org (2021-05-20 13:05:48)
>> On 2021-05-20 12:28, Stephen Boyd wrote:
>> >> Put dongle to D3 state so that it will not issue the unnecessary
>> >> second
>> >> irq_hpd with sink_count = 0. this will prevent the annoy but unharmful
>> >> DP_LINK_STATUS_UPDATED warning message.
>> >> Again, we can not disable hpd interrupt since dongle still attached
>> >> and
>> >> hdmi cable can be plugged in at any instant.
>> >>
>> >
>> > Right I'm not suggesting to disable hpd interrupt, just the hpd_irq
>> > interrupt once an unplug irq comes in, and do that in hardirq context.
>> > Also, I'm suggesting that we consider unplug as a higher priority if
>> > the
>> > hard irq handler is delayed for some reason and both an unplug irq and
>> > an hpd irq are pending in the hardware when the hard irq handler is
>> > running. Putting the dongle into D3 state won't fix these problems.
>>
>>
>>
>> The unplug interrupt is not happen in this case since dongle still
>> attached.
>> The unplug interrupt only happen when dongle unplugged.
>
> Agreed.
>
>>
>> I think you mistakenly think DP_LINK_STATUS_UPDATED is caused by
>> unplug
>> interrupt.
>
> Ok, got it.
>
>> DP_LINK_STATUS_UPDATED happen is due to dongle issue two consecutive
>> irq_hpd with sink_count = 0 when hdmi cable unplugged from dongle.
>> The first irq_hpd with sink_count = 0 is handled as expected to turn
>> off
>> display.
>> After that the second irq_hpd with sink_count = 0 is handled.
>> Since display had turned off, then there is nothing to do but spill
>> DP_LINK_STATUS_UPDATED warning message.
>> There is no unplug (hpd become low) happen in this case since dongle
>> still attached.
>
> Agreed.
>
>>
>> All interrupt (plug/irq_hpd and unplug) are required to be handled in
>> the order of happening.
>> We can not ignore any one.
>> For example, you plug/unplug two different resolution monitor
>> alternative to/from dongle and unplug dongle once for while.
>>
>> I think the race condition you describe here all had been taken care
>> with
>> 1) convert irq into event and store at event q in order.
>> 2) irq handled base on transaction. Next irq can be handled when
>> previous irq transaction is done.
>>
>
> I'm mostly trying to point out that the irq handling and masking needs
> to be done in the hard irq context and not in the kthread. It may or
> may
> not be related to this message that's printed.
>
> What happens if the hardirq is blocked by some other irq that takes a
> long time to process? Imagine this scenario:
>
> CPU0 CPU1
> ---- ----
> really_long_other_hardirq() {
> hpd_irq
> hpd_irq
> hpd low
> }
>
> dp_display_irq_handler() {
>
> <fork things to kthread>
> }
>
> Shouldn't we ignore any hpd_irq events in this scenario? And shouldn't
> we be disabling the hpd_irq by masking it with DP_DP_IRQ_HPD_INT_MASK
> when hpd goes low (i.e. DP_DP_HPD_UNPLUG_INT_MASK)?
1) irq_hpd interrupt always happen before unplug interrupt
2)if hdp_isr_status = (DP_DP_IRQ_HPD_INT_MASK |
DP_DP_HPD_UNPLUG_INT_MASK) at the time when read at
dp_display_irq_handler(),
then DP_DP_IRQ_HPD_INT_MASK will be add into evetn q first followed by
DP_DP_HPD_UNPLUG_INT_MASK be add into event q.
So that DP_DP_IRQ_HPD_INT_MASK will be executed by the event thread
before DP_DP_HPD_UNPLUG_INT_MASK.
On the other word, IRQ_HPD has higher priority over UNPLUG in the timing
matter.
By doing that we can shut down display gracefully.
If you insist, at hdp_isr_status = (DP_DP_IRQ_HPD_INT_MASK |
DP_DP_HPD_UNPLUG_INT_MASK) case,
we can have only add DP_DP_HPD_UNPLUG_INT_MASK to event q only by
dropping DP_DP_IRQ_HPD_INT_MASK.
Is this will work for you?
next prev parent reply other threads:[~2021-05-20 22:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 17:35 [PATCH v4 1/2] drm/msm/dp: handle irq_hpd with sink_count = 0 correctly Kuogee Hsieh
2021-05-18 21:42 ` Stephen Boyd
2021-05-19 16:01 ` khsieh
2021-05-19 21:06 ` Stephen Boyd
2021-05-20 16:08 ` khsieh
2021-05-20 19:28 ` Stephen Boyd
2021-05-20 20:05 ` khsieh
2021-05-20 21:28 ` Stephen Boyd
2021-05-20 22:39 ` khsieh [this message]
2021-05-21 5:00 ` Stephen Boyd
2021-05-21 15:21 ` khsieh
2021-05-21 19:18 ` Stephen Boyd
2021-05-21 19:45 ` khsieh
2021-05-21 20:54 ` Stephen Boyd
2021-05-20 20:36 ` khsieh
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